Carbon tinkering

So I am pursuing the production of carbon nanotubes. I have found easy success with arc discharge and something kind of like progress with a CVD rig I have patched together from another design, but I'm all about longer tubes (guess my gender for a gold star). Of course, longer tubes are the main goal of better educated minds than my own, but that is hardly going to stop me from tinkering. Bare with me as this is not well thought out yet.

Blast a cathode substrate with a charged carbon based inert gas. I want to use a magnetron to convert the gas to plasma so it will carry the charge of an anode nozzle thus directing the plasma flow towards the cathode. The concept being that the carbon would gather on the cathode substrate leaving the allotropes of carbon, then by taking advantage of the conductivity of the (hopefully) nanotubes I could lengthen the gap between anode and cathode thereby lengthening the carbon deposit.
I am not sure that I actually expect this method to work so for now this is just some fun brainstorming and I welcome all and any input or perhaps another direction or more information I could pursue.